1. Field of the Invention
The present invention relates to a substrate for a display device, a manufacturing method for the same, and a display device. More specifically, the present invention relates to a substrate for a display device that can be applied to a liquid crystal display device and the like, a manufacturing method for the same, and a display device that has such a substrate.
2. Description of the Related Art
At present, liquid crystal display devices have characteristics such as compact, thin, lightweight, and low power consumption, and have been widely used in a variety of electronic apparatuses. In particular, active matrix type liquid crystal display devices (liquid crystal display panels) having switching elements as active elements have display properties of the same level as those of CRT's (cathode ray tubes), and therefore, have been widely applied in OA apparatuses, such as personal computers, AV apparatuses, such as television sets, and cellular phones. Such liquid crystal display devices recently have been larger and improved in qualities such as high-definition and improvement of effective area ratio of pixels (high aperture ratio) rapidly. Therefore, further improvement in the performance of substrates for display devices used in display devices such as liquid crystal display devices has been required, and improvement in design, manufacturing technology and the like has progressed.
Active matrix substrates are widely used as substrates for display devices such as liquid crystal display devices. A manufacturing technology for an active matrix substrate where pixel electrodes and source lines (signal lines) are formed on the same plane on a substrate is known, and in the case where an increase in the definition and the aperture ratio is achieved according to this technology, the distance between pixels and source lines, the width of source lines and the like have been reduced, in order to increase the effective area of pixels. However, reduction of the distance between pixels and source lines easily occurs defect of short-circuiting, and reduction of the width of source lines easily occurs defect of disconnected wirings. That is to say, occurrence of defect of short-circuiting poses reduction in yield according to a manufacturing technology for an active matrix where pixel electrodes and source lines are formed on the same plane on a substrate, and there is room for improvement in this respect.
For this reason, manufacturing methods for a transmission type liquid crystal display devices characterized by the following (a) to (c), for example, have been proposed (for example, refer to Japanese Kokai Publication Hei-09-152625 (pages 1 to 3)) with respect to a manufacturing method for an active matrix substrate, in order to prevent defects caused by short-circuiting and disconnected wirings as described above, as well as in order to improve reduction of the yield.
(a) A (transparent) interlayer insulation film is provided after switching elements (active elements) and source wirings (source lines) have been formed.
(b) Switching elements are brought into connect with (transparent) pixel electrodes through contact holes.
(c) Pixel electrodes are formed on the interlayer insulation film, and thereby, source wirings and pixel electrodes are not disposed on the same plane.
A liquid crystal display device is manufactured by attaching a color filter substrate so as to face the active matrix substrate manufactured as mentioned above and by injecting liquid crystal between these substrates. As for the color filter substrate, a substrate where color regions of R (red), G (green) and B (blue), for example, are provided so as to correspond to the pixel regions on the active matrix substrate side, and in addition, a black matrix (light blocking film) is provided in the portion other than the respective pixel regions, may be used.
FIG. 13 is a schematic plan diagram showing one pixel in an active matrix substrate (thin film transistor array substrate) according to the previous art, and a portion of a pixel adjacent to the pixel. As shown in FIG. 13, the gate line (scan line) 101 and the source line (signal line) 102 are placed so as to cross each other in one pixel of an active matrix substrate 130. A thin film transistor (hereinafter referred to also as TFT) 114, used as a switching element, and the pixel electrode 103 are disposed in the crossing portion. The TFT 114 is formed of the gate electrode 104 connected to the gate line 101, the source electrode 105 connected to the source line 102, the drain electrode 106 connected to the pixel electrode 103, and the semiconductor layer 125 in island form. The drain extracting-electrode 106′ is connected to the pixel electrode 103 through a contact hole 109. In addition, the lead out drain electrode 106′ faces a common capacitance line 107 with an intervening gate insulator 111, and thus, an auxiliary capacitor is formed.
Next, a manufacturing method for an active matrix substrate, particularly a thin film transistor array substrate, is briefly described with reference to FIGS. 13 to 17. FIG. 14 is a cross sectional diagram of the thin film transistor array substrate along line H-H′ of FIG. 13, and FIG. 15 is a cross sectional diagram of the thin film transistor array substrate along line I-I′ of FIG. 13. FIG. 16 is a schematic plan diagram showing terminals for leading out gate lines, and FIG. 17 is a schematic plan diagram showing terminals for leading out source lines.
When a thin film transistor array substrate is manufactured, first, the gate lines (scan lines) 101, the gate electrodes 104 and the common capacitance lines 107 are simultaneously formed by means of film formation, photolithography and etching on a substrate 110 made of a transparent insulating substrate, such as glass.
Next, thereon the gate insulator 111, the active semiconductor layer 112 and the low resistance semiconductor layer 113 made of n type amorphous silicon or the like are formed as films which are then converted to the island form 125 by means of photolithography and etching.
Next, the source lines 102, the source electrodes 105, the drain electrodes 106 and the lead out drain electrodes 106′ are, simultaneously formed by means of film formation, photolithography and etching, and subsequently, the low resistance semiconductor layer 113 are separated into sources and drains through etching.
Next, the lower interlayer insulation film 120 made of SiNx or the like are formed as films so as to cover the entire surface, and subsequently, the upper organic interlayer insulation film 115 made of a photosensitive acryl resin or the like are formed by means of photolithography so as to have a pattern for contact holes 109, a pattern for contacts of the terminals for leading out gate lines (X in FIG. 16), and a pattern for contacts of the terminals for leading out source lines (Y in FIG. 17).
Next, the lower interlayer insulation film 120 and the gate insulator 111 are sequentially etched by using the upper organic interlayer insulation film 115 as a mask, in order to form the contact holes 109, the terminal for leading out gate line 200 and the terminal for leading out source line 300.
Next, the pixel electrodes 103, the uppermost layer electrodes 201 of the terminal for leading out gate line 200, and uppermost layer electrodes 301 of the terminal for leading out source line 300 are formed so as to cover the contact holes 109, the terminal for leading out gate line 200 and the terminal for leading out source line 300. The contact holes 109 allow the drain electrodes 106 in TFT's 114 and the pixel electrodes 103 to be connected to each other through the lead out drain electrodes 106′.
According to such a manufacturing method, the source lines 102 and the pixel electrodes 103 can be separated from each other with the intervening interlayer insulation films 115 and 120 in the active matrix substrate. Separation of the source lines 102 from the pixel electrodes 103 can prevent reduction of the yield caused by short-circuiting between the pixel electrode 103 and the source line 102, and at the same time, as shown in FIG. 13, the pixel electrodes 103 and the source lines 102 can be overlapped, resulting in improvement in the aperture ratio of the liquid crystal display devices or the like.
According to the above described manufacturing method for a substrate for a display device, however, in the case where a defect on the upper organic interlayer insulation film occurs, the lower interlayer insulation film and the gate insulator are etched from the film defect portion and short-circuiting occurs in a pixel electrode formed on the upper organic interlayer insulation film and therefore, there is room for improvement in terms of preventing defects in display, reductions in the quality of the display device, and in the yield.
A technology for making the gate insulating layer to have a two-layer structure formed of an oxide insulating layer produced by oxidizing a metal film and a gate insulator has been proposed for a previous substrate for a display device (for example, refer to Japanese Kokai Publication Hei-03-153217 (pages 1 and 3)). When a gate insulating layer has multiple layer structure according to this technology, however, effects of preventing defects of short-circuiting due to a defect on an interlayer insulation film cannot be obtained, when the insulating film existing lower than the uppermost layer is removed by etching with the uppermost interlayer insulation film as a mask. In addition, this technology provides measures against the defect of the gate insulator, and does not provide measures against the defect of a pixel caused by electrical leakage caused by the defect of the insulating film that exists between wirings, such as gate lines and source lines, and pixel electrodes in a substrate for a display device where the pixel electrodes are formed on the interlayer insulation film.